This weekend marks a huge milestone in American motorsports: it’s the 100th running of this country’s greatest spectacle of speed, the Indy 500. And when it’s over, you’re going to see a lot of milk-chugging from the winner.

Tradition is everything at the Indy 500, and the winning driver downing a bottle of sweet, sweet victory-milk is one of the oldest and strangest. It started in the 1930s and became a race mainstay by the 1950s, although not every winning driver has done it—much to the chagrin of the crowd.

Where does this tradition come from? Why do people still do it? And what kind of milk do they drink? All of your questions will be answered in this explainer video.

Who’s going to down the milk this year?

Video Production & Animation: Elisa Solinas/Gawker

Scott Dixon, winner of the 92nd running of the Indy 500 in 2008, chugs a bottle of the good stuff. Photo credit Getty Images